1. Field of Invention
The invention relates generally to investigating an annulus between tubulars disposed in a subterranean wellbore. More specifically, the present invention relates to a device and method that uses a radiation source for inspecting a subterranean annulus and a radiation detector for identifying a substance or substances in the annulus.
2. Description of Prior Art
Subterranean wellbores used for producing hydrocarbons typically are lined with a string of casing that is cemented to the formation intersected by the wellbore. Often an inner casing string is inserted within the casing string cemented in place. Fluid produced from the well flows to the surface within production tubing that is inserted into the inner casing string. Over the life of a typical well the production tubing may be removed so that remediation, repair, or flow enhancement operations may be commenced in the well. There may also be a need at some time for removal of a portion or for all of the casing.
Generally drilling fluids fill the annular space between the concentric tubulars. Particulates within the drilling fluids may settle out or precipitate over time and form a cement like substance that couples together the concentric tubulars and prevents the removal of the inner tubular from the wellbore. While cutting tools can sever the tubulars to enable removing the unstuck portion, the tubular cannot be removed if the cut is made at a depth below where the tubulars are adhered together. Alternatively, too shallow a cut can leave an undesirably long portion of free pipe extending above the point of adhesion.